The first sanitize stripped only the ESC byte, leaving visible '[1m[37m'
halves as noise. Strip full CSI/escape sequences first (while ESC is
present), then residual control bytes — clean text.
And read the log: a box sitting at 'GNU GRUB / Press enter to boot /
UEFI Firmware Settings' never booted — that is the IMAGE, not box. Say
so, and point at re-pulling the image or pinning BOX_IMAGE. Surfaced
running the 0.5.0 drill after --purge-storage re-downloaded a
debian/13/cloud build that hangs at the GRUB menu on the serial console.